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shakey, i understand about the 1667 ohms bit, but, shouldnt it be lower than that (exact figure not known at mo) to do away with an unreliable earth path??

depends what you mean by 'do away with'

No value would allow you to do away with an unreliable earth

Or are you refering to the value of 200 ohms for TT earth electrodes?

This is the max value at which it could be condidered a 'stable reading', but is not a max value as far as the RCD is concerned

there is no 'leeway' for an unreliable earth
 
Technically an RCD will operate without any form of earth path being installed. It operates. as stated in other answers, by monitoring the phase and neutral and reacting to an imbalance between them. Normally this imbalance is as a result of an "earth fault" be it to a back box, cpc, or as a result of external influences like moisture. It is possible to have a created imbalance, for example where wall lights have been installed and the live is taken from the lighting circuit and the neutral is taken from a socket on the final ring circuit protected by an RCD (16th edition style split load board with protected and unprotected ways). By switching the wall lights on an imbalance is created on the final ring circuit which will trip the RCD. Whilst not a common fault it is a typical "lash up" job by a "Barry the Bodger".
 
Technically an RCD will operate without any form of earth path being installed. It operates. as stated in other answers, by monitoring the phase and neutral and reacting to an imbalance between them. Normally this imbalance is as a result of an "earth fault" be it to a back box, cpc, or as a result of external influences like moisture. It is possible to have a created imbalance, for example where wall lights have been installed and the live is taken from the lighting circuit and the neutral is taken from a socket on the final ring circuit protected by an RCD (16th edition style split load board with protected and unprotected ways). By switching the wall lights on an imbalance is created on the final ring circuit which will trip the RCD. Whilst not a common fault it is a typical "lash up" job by a "Barry the Bodger".

yup, done a few like that Tony

"just installed a new circuit, RCD trips as soon as i switch it on"

Investigation finds that the guy didnt know there was seperate neutral bars:eek:

Doh!
 
Not sure certain CU manufacturers are aware of this fact either! I've found several new CU's to have the neutrals connected arbitrarily to whatever bar suits at the time of manufacturer.
 
Modern (current controlled) RCDs make the assumption that any imbalance in line and neutral currents must be flowing to earth (because generally there isn't anywhere else for it to go) they don't actually measure anything with reference to the main or cct cpc's. However it still doesn't remove the fact an earth path must be present or there would be no residual current and the device would not operate.
I think the older voltage controlled ELCBs sensed voltage on the cpc but they were effectively proscribed in 1981 as it was realised that a parallel earth path would render them inoperable under true fault conditons.

Ask your man to draw out the FULL fault path and ask him were exactly does he thinks that inconvenient stray, 'residual' "I delta n" tripping current is going.
 
Hiya guys will an RCD or RCBO work if there is no earth in the house?A fellow worker said to me today that there is no need for an earth in a house if the board has an RCD or is controlled by RCBOs as they work on the inbalance of the live and neutral.


what about disconnection times?
 
The Only THEORETICAL reason that I can think of is that, if the fault trip coil on the RCD was to become faulty and the RCD did not trip then the touch voltage on a faulty piece of equipment may rise above 50V. Thus EEBADS would come into play.

:rolleyes:
 
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The Only THEORETICAL reason that I can think of is that, if the fault trip coil on the RCD was to become faulty and the RCD did not trip then the touch voltage on a faulty piece of equipment may rise above 50V. Thus EEBADS would come into play.

:rolleyes:

SteveF1 gather you have not done the 17th yet as there is No such thing as EEBADS any more its ADS
 
SteveF1 gather you have not done the 17th yet as there is No such thing as EEBADS any more its ADS

ian.settle1
Your assumption that I have not done the 17th Edition is incorrect. Yes you are correct that EEBADS has been replaced by ADoS as an acronym buit there will always be EEBADS. Although it is not refered to in the 17 Edition it does not mean "ther is no such thing any more" Equipotential bonding will always be required where protection against electric shock (indirect contact) is provided by Earthed Equipotential Bonding and Automatic Disconnection of Supply (EEBADS).It will also be used where disconnection times for circuits cannot be met, and where circuits with differing disconnection times come from a common distribution board.
I think you missed the point of the original post.
Hiya guys will an RCD or RCBO work if there is no earth in the house?A fellow worker said to me today that there is no need for an earth in a house if the board has an RCD or is controlled by RCBOs as they work on the inbalance of the live and neutral.

Regards
Steve F1:cool:
 
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